FIELD OF THE INVENTION
The present invention relates to stabilized halogen-containing resins, and more particularly thermally stabilized compositions of halogen-containing resins.
It is well known that when halogen-containing resins, including polyvinyl halide and halogenated polyolefin are subjected to exposure to sunlight or to elevated temperature during or after compounding or processing, they undergo marked change in color and transparency and become brittle owing to occurrence of a decomposition reaction which is mainly attributable to release of hydrogen halide. A number of stabilizers have been proposed for preventing said deterioration. Among these stabilizers, those which exhibit excellent stabilizing effect are organo tin compounds and cadmium and lead soaps. However, the use of these is limited because of their high toxicity. Calcium and zinc soaps which are low toxic stabilizers exhibit inferior thermal stability as compared with cadmium soap.
Thus, the development of non- or low toxic stabilizers exhibiting excellent thermal stability has been eagerly sought.
It is an object of this invention to provide an improved thermally stabilized halogen-containing resin composition. Another object of this invention is to provide an improved thermal stabilizer having low toxicity.
It has also been known that salts of N-aliphatic acyl or aromatic acyl derivatives of neutral or acidic amino acids with divalent metal are useful as stabilizers for halogen-containing resins (Japanese Patent Publication No. 16109/1974). It has been found, however, that the halogen-containing resins stabilized with these N-acyl neutral and acidic amino acid salts have some deficiences, particularly in respect to color and transparency. Initial discoloration occurs rapidly at the usual processing temperature of 160.degree. to 190.degree.C.